The main character in the "The Sniper" is the Republican sniper. Very little direct characterization is done by the author, so much of the reader's impressions of him come from how he acts.
Physically, we know that the sniper is male. We know that he is thin and young looking as well because the story tells us those details.
His face was the face of a student, thin and ascetic, but his eyes had the cold gleam of the fanatic.
More than likely, the sniper is young, but it is possible that he simply looks like a young student as well. As for being thin, that is probably a result of not being able to get a minimum calorie intake during wartime. The rest of the above quote gives readers a look into the sniper's personality. "The cold gleam of the fanatic" tells us that the sniper is passionately devoted to one of two things. First, he could be devoted to the cause. Second, he could simply be a fanatic about killing people, and that is why he is a sniper. Either way readers will quickly learn that he has no problems shooting and killing unarmed combatants.
I believe that the sniper is quite brave. Once he is under fire from the enemy sniper, he could have decided to extricate himself from his discovered position; however, he successfully kills all three targets while under fire. The firefight also shows readers that the sniper is cool, calm, and capable of creative thinking while in an incredibly tense situation because he thinks of a way to fool the other sniper into committing a mistake that costs the enemy his life.
The titular sniper, who is not given a name, is a young Irishman. We are told little about him directly; most of his characterization comes from the description of his actions, and what he looks like, not necessarily who he is, or was, before the war. This is probably intended to diminish his individuality, with the purpose of making him a representative of virtually any young man in the war.
The first description we are given of the sniper is that he has the "face of a student, thin and ascetic". While allusions to a student may draw up the idea of youth and innocence, the use of the descriptors "thin and ascetic" (ascetic meaning self-disciplined) implies that a better term might be scholarly or spartan. Meanwhile, his eyes have the "cold gleam of a fanatic". This implies that the sniper is at war without and within; his self-control tempers a fierce personal motivation.
We can surmise that this is not the sniper's first battle; his careful evaluations of the risks of each action imply that he has done this before, and perhaps seen the consequences that befell others less fortunate than himself. This is also suggested by his ability to care for himself after he is shot, and to overcome the pain of his injury by the force of his own will.
For much of the story, the sniper functions as an embodiment of self-control and restraint, but this veneer is cast aside when the tension has abated, and the sniper is suddenly overcome with disgust. He is, after all, only human, and can only stave off his own emotions for so long under this kind of pressure.
Overall the sniper is meant to be someone we can relate to; who behaves as we might wish we could behave under the circumstances, but who also has realistic weaknesses and makes mistakes. This reinforces the purpose of leaving the sniper unnamed; the reader can put themselves in the sniper's place, and see themselves behaving in the same way.
The sniper is a young man in the Republican army in Dublin, Ireland. He is a hardened character who has been through life-or-death situations many times as a member of the army. He is an adept soldier and is crafty, observant, and efficient. He has gotten so used to killing people that it hardly phases him anymore at the beginning of the story. However, after he has shot and killed 3 people, his attitude changes. He becomes disheartened and angry about the fighting and death that he has been around constantly. Enotes states that he rarely makes poor decisions, but he decides to find out the identity of one of the people he shot on the street. When he goes to check, he realizes that he has shot and killed his own brother.